The short answer is that Vlingo is an extremely powerful application, and while its setup process attempts to shield the user from as much complexity as possible, it's unavoidable in certain situations – particularly with some BES configurations.
Vlingo uses many of the core functions of your BlackBerry to capture your voice, send and receive data, dial the phone, send email and text messages, access the address book (for voice dialing, emails, and text messages), and work with Bluetooth headsets. In order for Vlingo to work, it needs permission to access these functions. If your phone is configured to a corporate BlackBerry Enterprise Server (BES), you're particularly likely to encounter a number of prompts while setting up Vlingo.
Depending on your configuration, you may be prompted several times. If you respond to these prompts by checking the Do not ask me again box and then clicking Allow, the prompts will stop showing up.